The present invention relates to bismuth substituted iron garnet crystals for use in magneto-optic light deflection systems, such as described in U.S. Pat. No. 3,752,563, and more specifically to bismuth substituted iron garnet crystals having large values of Faraday rotation (F) and low coefficients of optical absorption (.alpha.). In previously filed applications Ser. No.'s 817,754, now abandoned, and 954,511, assigned to the present assignee, a melt solvent and a rinse melt are described for growing mechanically superior crystals. While previous work has produced crystals having relatively large Faraday rotations by promoting bismuth substitutions in the garnet's lattice such as suggested in the articles of Hiroshi Takeuchi, et al., J. Appl. Phys., Vol. 44, No. 4789 (1973); D. E. Lacklison, et al., Solid State Commun., Vol. 14, 861 (1974); and U.S. Pat. No. 4,092,208 issued to Brice, et al., the optical absorption qualities of the bismuth substituted crystals in the near-infrared region (0.70 to 1.60 microns) have been relatively uncontrolled.
Single crystal work done by D. L. Wood, et al., with calcium doped yttrium iron garnet (YIG), J. Appl. Physics, Vol. 38, No. 3, 1038 (1967), and J. Appl. Physics, Vol. 37, No. 3, 1232 (1966) suggests that introduction of calcium Ca.sup.2+ and silicon Si.sup.4+ into a YIG garnet melt with a PbO-B.sub.2 O.sub.3 flux can affect the .alpha. of the single crystal depending on the concentration of Ca.sup.2+ and that the minimum .alpha. can be shifted by adding Si.sup.4+ to the melt. The present invention, however, teaches that an improved bismuth substituted iron garnet crystal can be grown on a GGG substrate by combining Lutetium (Lu.sup.3+) and calcium (Ca.sup.2+) in a melt containing a lead oxide (PbO) bismuth oxide (Bi.sub.2 O.sub.3) flux, thus promoting bismuth substitution and enabling a low growth temperature, to obtain a deflector crystal having a high Faraday rotation and a relatively low optical absorption coefficieht .alpha..
It is therefore an object of the present invention to grow crystals from a melt containing bismuth oxide to enable substitution and a high Faraday rotation.
It is a further object to grow crystals on a substrate from a melt containing lead oxide to enable a low growth temperature and still reduce the optical absorption of the crystals.